Annular element antenna systems



y 5, 1956 c. A MARTIN 2,746,040

ANNULAR ELEMENT ANTENNA SYSTEMS Filed May 20, 1950 2 Sheets-Sheet 2 INVENTOR Char] sAMarZjII United States Patent ANNULAR ELEMENT ANTENNA SYSTEMS Charles Andrew Martin, Setauket, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application May 20, 1956, Serial No. 163,313

22 Claims. (Cl. 343839) The invention relates to antenna systems and it particularly pertains to wide-band, omni-directional antennas particularly useful for radio navigation applications.

For navigation purposes, the antenna must not only be capable of radiating at high efiiciency but :also must radiate a band of frequencies sufliciently Wide to properly reduce the very short pulse envelopes involved. The

prior art antenna arrangements, when designed for high efficiencies, also exhibit very high figures of merit .(Q), and therefore are inherently narrow banded, especially at the very low and low frequencies usually employed for such services.

It has been suggested that a top loaded or umbrella antenna having dimensions at which the vertical portion is relatively short with respect to wavelength and therefore is traversed by substantially constant current and the top loading element has a relatively large radius, thus inherently setting up in effect a circular slot between the earth and the circumference of the umbrella which is relatively narrow in terms of the operating wavelength. It has been found, however, that such antenna arrangements are not capable of the required performance. One reason is that the Q of such an antenna remains too high in value. The radiation resistance of the suggested arrangement has been found to be nearly equal to that of a short top loaded vertical antenna of the same height. As to other requirements, one proposed low frequency navigation system requires the transmission of a :kc.-/s. bandwidth at 100 kc./s. The antenna Q must therefore be about 10 or less. Assuming that impedance correction can be realized efficiently by commonly used lumped circuit networks, to meet that requirement, a base insulated tower type vertical antenna would have to =be about 1200 feet high. Even then-the antenna elficiency would likely be not more thanSOper-cenL-mainly because of tuningcoil losses. The costs.anddifiicultiesinvolved in theconstructionof such a tower, especially :in :the far north regions, are very great.

Also, in order to :obtain substantially -.unidire,c.tional radiation of vertically polarized waves, termed ftheta polarization by standards established by-the :IRE, ifrom high-speed aircraft, I a modification. of-the abovermentioned annular slot antenna has been employed. The slot 'is normally located on .the underside of the fuselage or .wing. Since space in an airplane is always at a premium, it is highly desirable, and sometimes absolutely-necessary, that the cavityback of the slot'be'thin in'comparison'with a wavelength. That) of the antenna is then'high for-the same reason that the Q of a low umbrella antenna is high. However, the service usually requires that the bandwidth be quite large. Thus external impedance correcting networks are required to compensate for the detrimental effect of the .thincavity. The extent to which the networks can accomplish that purpose is limited: the circuit :par-ameters introduce power losses and weight and are .usually-diflicult to= design.and:critical to adjust.

2,746,040 Patented May .15, 956

Accordingly, it is an object of the invention to provide an antenna having high radiating efliciency and low factor of merit, or Q.

It is another object of the invention to provide an omnidirectional antenna for transmitting or receiving a wide frequency band at the very low and low frequencies.

It is a further object of the invention to provide a wide band, omnidirectional antenna having a very low factor of merit at very low and low frequencies.

It is still another object of the invention to provide an annular radiator -or receptor element for an antenna in accordance with the foregoing objects and having means to transform the effective driving resistance value to a value at which a low impedance transmission line may be employed.

It is a still further object .of the invention to provide an annular surface element .of interconnected spaced conductors having a folded dipole type feed to provide an input impedance ,of high ohmic value.

It is yet another object of the invention to provide an antenna having an annular radiator .or receptor element arranged in conjunction with a ground plane element to provide a high ohmic input impedance.

It is yet a further object .of the invention to provide a compact .wtenna structure for use on metal clad vehicles which will have low Q and wide band width.

These and other vobiects of the invention which will appear as the specification progresses are achieved by means of .anautenna structure having anaunular surface radiator 0r receptor element arranged with respect to a ground plane element in conjunction with which ,it is to work. The radii of inner and .outer peripheries of the annular.surfacerelementare of such value that the proper feed point impedance .isofiered to the associated .aPParatus. Preferably :the annular element is composed of radially arranged conductors having :the outer ends connected together and anurnber of the inner ,ends taken ;in regular .orderabout the center coupled to :transducer apparatus with the remaining conductor ends connected to the ground plane element toprovide a folded dipole characteristic.

,The invention will .be described with reference to the accompanying drawing forming a part of the specification and in which:

Fig. .l is anillustrationof a fundamental arrangement of an antenna ,accordingto the invention;

Fig. 2 is an illustration :of an alternative-arrangement of an antennaaccording to the invention;

Fig. 3 is an illustration v ofa practical low frequency antenna according to the invention;

Fig. 4 .is an illustrationof another antenna according totthe invention;.and I .Fig. 5 is an illustration-of an alternativeembodiment of an antenna according tothe invention for use at very high frequencies; ,FigpSabeing a plan view andrFig. 5b being across-sectional;elevationview of the embodiment.

Referring to :1, there is shown schematically an antenna arrangement according to the'invention .Wherein a number of conductors ZO-are radially arrangedinaplane with the inner ends connected by a conductivetring 22 having a radius l, forming the inner boundary, and the-outer end conuectedbyan-outer conductive ring 2,4, formingthe outer boundary, havinga radius {I -he conductors thus lie within :the confines of an annulus. The structure, according to the invention, is based on an annular conductive surface as follows from "the definition to be foundin the Mathematics Dictionary, edited by James andlarnes, and-publishedbyiD. yan Nostrand Co. in 1949: ;annulus.;the portion of a .plane bouuded bYztWO concentric :circles inttheplane. The foregoingconductors;are:spaced a distancesh from .the surface of'rthe earth or a conductive surface connected to ground or some fixed reference potential. Frequently, where the natural surface of the earth does not form an efficient ground, conductive members 23 are provided, preferably buried in the earth as indicated. Radio frequency apparatus, shown here as a generator 26', may be coupled between conductor 22 and conductive members 28 by means of a down lead conductor 30. Preferably, however, several generators 26 are connected about the periphery of conductor 22 to provide a uniform distribution of power between the generators and conductors 20. In such an arrangement, the conductor 22 may be omitted if desired without disturbing the inner boundary of the conductive annular surface. In the interest of keeping power loss in the system at a minimum, by elimination of tuning coils, and to realize minimum Q the ratio between the radii of conductors 22 and 24 should be such that the conductive system is resonant.

Experimental results obtained with the above-described arrangement form the basis for one plausible theory of operation. A diverging spherical wave is set up between the surface of feed wires 30 and the flat surface effectively formed by conductors 20. Then a cylindrical wave is sct up from the inner circumference on out, between the surface of members 20 and the earth or members 28. The electrical effect is that of adding an inductance component in series at the feed point of the arrangement. This effect can be employed to good advantage as will be shown hereinafter. The results obtained appear to justify further theoretical investigation on the basis of the assumption of a pure cylindrical wave in the space between an inner perfectly conducting cylinder and an outer fictitious perfect magnetic conductor forming a cylinder at the outer edge of the annular conductor. As would be expected, there is some spreading of the electric field. To account for this spreading, the effective radius of conductors 20 7 should be taken as the outer radius R2 plus the height h.

As stated above, the structure shown in Fig. 1 has been employed to radiate wave energy and of course reversed operation as a receiving antenna is understood. Two models were operated at 200 and 275 mc./s., respectively. In both of these models radius R1 was 1 centimeter and radius R2 was 15.6 centimeters, The height h and 2 and 5 centimeters, respectively. In both instances the ground plane conductor was approximately 12 feet square. These model arrangements are suitable for high frequency application as well as for scaling low frequency installations as will be shown hereinafter.

- For lower frequency applications, particularly the very low and low frequency ranges, an antenna according to the invention is readily realized by employing the basic arrangement shown in Fig. 2. For clarity, the ratio of height to diameter is exaggerated all out of proportion in the drawing. Conductors 20 of Fig. 2 are arranged substantially as in the arrangement of Fig. 1. Additional radially arranged conductors 32 connected at the outer ends to conductors 24 and lying substantially in same plane as conductors 20 are connected at the inner ends to the ground plane conductors 28 by down leads 34. The ground plane element is constituted by radial buried conductors 28 and the earth in which they are in contact.

Conductors 28 may be conveniently connected together at the innermost end by a conductor 36 if desired.

Radial conductors 32 are connected at the outer ends to conductor 24 and have the inner ends connected to down leads 34 which are connected to grounded conductor 36. Such an arrangement provides advantages similar in effect to those obtained by the folded dipole antenna over the single dipole element, as described by P. S. Carter in his U. S. Patent 2,283,914, issued May 26, 1942. In ge'neral, this method of coupling provides increased bandwidth and substantially lower values of Q.

In actual practice it is undesirable to use more than one generator for obvious reasons. A simple single source feed arrangement would be to couple a number of transmission lines of equal length and running radially to the terminals 33. As an alternative having decided advantages, the arrangement depicted in Fig. 3 is suggested. Conductors 20 and 32 are all connected together at the outer extremities by conductor 24. The inner extremities of conductors 32 are led to ground by conductors 34 and those of conductors 20 are led to generator 40 by conductors 42 arranged in conical configuration. Generator 40 has one terminal grounded by conductor 36 as shown. In practice, however, individual ground connections are contemplated for each conductor.

An important advantage of this method of feed is that it has an impedance correction characteristic. Effectively, there is an anti-resonant loop connected between each feed point and ground. That is just what is desired to reduce the slope of the reactance vs. frequency curve associated with the antenna. On account of this, less expensive antenna designs than heretofore obtained are made possible. In Fig. 4 there is shown an alternative arrangement wherein down leads 42 of Fig. 3 are interchanged with down leads 43 having vertical portions 43'. The impedance relationship can be varied by changing the ratio of condoctors 43 and portions 43. One of the principle advantages of the antenna according to the invention is that each of the driven down leads may have an inductancecapacity circuit interposed therein to permit correction for variation of the reactance slope by the use of conventional and readily available circuit components.

The practice of the invention at very low and low fr quencies is contemplated with plant construction only slightly ditferent from those presently employed. Six poles or towers are contemplated with conductor 24 suspended therefrom by triadics. The transmitting or receiving apparatus may be located at a distance and connection made by means of a coaxial cable or cage type transmission line, although the use of any other known transmission line is possible.

It should be stressed that the antenna according to the invention is not intended as a height eliminator, but rather as one which minimizes the disagreeable effects of low heights. Since ordinarily a radial ground system presents a small part of the total cost of an antenna system, the installation of one extensive enough to give efficiencies in the order of per cent would be entirely feasible with reasonable antenna heights at a frequency of kc./s.

At high and ultra high frequencies the practice of the invention will produce arrangements of somewhat different structural appearance. This is to be expected especially in applying the invention to aircraft installations. For example, in the embodiment shown in cross section in Fig. 5a, the metal skin 70 of the aircraft constitutes the ground plane element and is more often than not a curved rather than a plane surface. However, the antenna according to the invention can be efficiently operated under such conditions. A cavity resonator element 72 is arranged in the skin 70 of the aircraft behind a circular aperture having a radius R3. An insulating disc member 74 of radius R3 is arranged in the circular aperture to form a cover and is preferably shaped to conform to the surrounding aircraft structure. A wire ring 76 having a radius R2 and a number of radially arranged wires 7% and 79 are embedded in member 74; at a radius R1 wires 78 pass through holes in member 74 and converge toward wall 81 of cavity resonator 72. At this point they join the center conductor 82 of a coaxial transmission line 84 having a sheath conductor 86 connected to wall 81. Wires 79 then converge to join wall 81 at the point of connection of sheath 86. While conductors 76, 78 and 79 are shown on the outer side of disc 74, they may be placed on the inner surface with equal effectiveness. As shown the conductors are embedded in the disc 84 and are flush with the outer surface 70, but another alternative would be to apply a thin layer of conductive material in the desired configuration on the underside of disc 74. Also the radial Wires 78 may be connected to center conductor 82 of the transmission line 84 by a radially arranged transmission line assembly comprising a plurality of coaxial transmission line sections having the sheaths bonded to wall 81 and the center conductors continuing beyond the sheaths and directed vertically to connect to wires 78 at the radius R2.

While the arrangement of Fig. 5 is shown in the same relative position as are those of Figs. 1-4, in practice it may be used in any position. In aircraft installations it would more often than not be found inverted and in stalled on the underside of the airframe. Although the slot 74 is annular ratherthan cylindrical as in the longer wave embodiments, the field patterns obtained with both types do not differ greatly.

An antenna system as shown in Fig. 5 has several advantages for airframe installation. It is possible to reduce the thickness of the cavity 72 greatly over those of prior art arrangements. Since space in an airframe is always at a premium, this is a most important feature. The annular disc eifected by radial wires can be also arranged to obtain the impedance multiplying effect of the folded-dipole type feed. This brings the resonant frequency resistance of the radiator to a value more nearly that of the characteristic impedance of commercial cables, predominantly at 50 ohms. This construction also combines the Q lowering effect of the folded-dipole type feed and that of the feeding out from the center arrangement of the antenna according to the invention. Both effects are helpful in eliminating or simplifying any external corrective network required.

While the foregoing description is adequate as a basis for research in the practice of the invention, it is believed that the following discussion of various factors will prove helpful to the artisan.

The radiation resistance follows the approximate formula:

1601r (h/A) (1) The symbols are defined in the appendix. Formula 1 will be recognized as also being that of the top-loaded vertical antenna. The correlation of the two is simple. The radiated field can be determined either by considering the current in the vertical position or by assuming a more uniform distribution of magnetic dipoles about a small ring with the vertical radiator as a centerthe moments being directed along the circumference and the total moment being in direct relationship with the input current. If the top loading hat is increased in radius to effect a large horizontal disc type radiator, the field of this antenna is determined by assuming a ring of magnetic dipoles about the circumference of the disc. Then, if the input current is maintained the same as before, the total moment is equal to the total about the small ring assumed for the original vertical. Moreover, if the radius of the disc is not much more than 0.2 wavelength, the field of the final radiator is practically the same as that of the original. Since feed point radiation resistance is fundamentally the total power radiated per unit ampere of input current, it follows that its magnitude is nearly the same for the disc as for the short top loaded vertical. Furthermore, introducing an aperture in the disc to change it -to the washer shape according to the invention does not alter the radiated field appreciably.

In the following it is assumed that conductivitiesof the annular element and the ground are infinite and the effect of radiation negligible. An outward travelling cylindrical wave totally reflected at the outer rim is also assumed. Actually the height being small compared to a wavelength, -the end eifect causes the disc to act as though the outer radius were increased by a length equal approxiinately to the height 'of the element shave the earth.

and input reactance:

V 041 JNROYK Z) o( 1) 1( 2) 1 0 1 1( 1) 1( 2) 1( 1) 1( 2) In most short vertical antenna systems a large part of the power is lost in tuning coils. Equation 4 shows that the necessity of tuning can be eliminated by proper selection of R2 in relation to R1. Minimum Q can be realized when the antenna is resonant. In cases where lateral expansion of the antenna is not too costly, it is, therefore, desirable to design the antenna so that it is resonant--or nearly so. That condition is assumed in the remaining parts of this discussion.

The radiation field is given by:

E9=KJ1(R2 sin 0) The directivity accordingly is:

jg /wma sin a) sin a do and the directivity loss in reference to a short vertical antenna is of computation the integrand is expanded and integrated term by term. The resulting expression is:

J. '(R sin (9) sin 0d0 (7) At resonance:

Since the ground currents of the antenna according to the invention are less concentrated than those of prior art arrangements, it might be expected that the ground losses would be relatively low. The ratio of power lost in the earth to that radiated is:

Comparison with Equation 9 serves to illustrate the favorable effect that increasing the inner radius R-i has on the antenna efiiciency.

Actually, Equation 10 which is strictly correct only for homogeneous and highly conductive earth, is not of great practical importance since the ground system would probably consist of a large number of radial wires. If the inner radius of the annular member is increased wit out increasing the number of radials, the ground loss might increase because the distance between wires is then larger. In order for Equation 10 to hold, the effective plating of the ground must be maintained by increasing the number of radial ground wires as radius R1 is increased.

The efiiciency of a given antenna according to the invention with a radial wire ground system is:

X100 per cent (11) The number of wires used to approximate the annulus of the antenna should have little effect on the radiation resistance. It will, however, affect the input reactance and so the Q of the antenna. A rough idea of the eifect may be obtained from the study of the characteristic impedance of a plane grating of wires 11 meters above an infinitely conductive sheet as compared to that of two infinitely conductive sheets, s meters apart. When 21rh/S 3,

the ratio of two characteristic impedances is approximately:

8 1n Z (27755) 12 1+ 27h The antennas radiation resistance is bound to be very low because of the antennas low height. The reduction in Q by the method of feed, is caused by the anti-resonant loop, in effect, which is connected between each feed point and ground. The impedance characteristic of such a loop is just what is required to reduce the reactance vs. frequency slope of the antenna at resonance. Since it is desirable that the feed resistance match the composite characteristic impedance of the radial transmission lines and also that it be reasonably high, a Wide lattitude of choice of values for N and in is available, even for a predetermined radiation resistance.

While the invention has been described in terms of specific embodiments, it is to be understood that other arrangements and modifications will be suggested to one skilled in the art without departing from the spirit and scope of the invention.

APPENDIX Two practical antennas according to the invention Antenna A Antenna B Units 160 0 feet.

0. 0163 0. 0204 O. 417 0. 653 ohms. 0. 326 0. 408 0. 031 0. 0183 305 180 feet.

0. 202 0. 176 19s? 1732 7 feet.

O. 774 0.196 ohms. 35. O 67. 9 45. 7 L 76. 9 percent.

5 10. 43 10. 43 ohms.

Note that in each case R1 represents a good match to five 50 ohm cables.

Symbols employed in the foregoing specifimtion i=\/ 1r=3.1416 w=21r times the frequency f trequency fo=frequency of resonance c=velocity of light \=wave1ength=c/f n permeability of free space and of ground 41r l0 g conductivity of the earth or ground plane element E :KeEO 1 =dielectric constant of the earth or ground plane element A=j /Ke-jl8g 10 f =\/i +i zintrinsic impedance of the ground H efliciency K --a constant =radial distance from the center of the washer z outer radius of the washer 1=inner radius of the washer R: (Z-Ir/A p R2: Z1r/ p2 R1: (21r/ p1 h=height of the annular ground plane Jn=BBSS6l function of first kind of order n (14) Yn=Besse1 function of second kind of order n (15 I p) :radial current in the washer at R. M. S. Io=radial current at inner rim of washer, I( R. M. S. V( :potential of washer at R. M. S. Vo potential at inner rim of annular R. M. S. Rr=radiation resistance X=input reactance Z =R+ jK :input impedance R y=feed resistance Re=resistance associated with ground loss Q factor of merit defined by reactive power/ active power We=power lost in the earth Wr power radiated Pe power lost in the earth per unit radial distance Pm :power lost in the ground wires per unit radial distance Re=resistance associated with ground system loss mw=number of overhead wires in radial wires element mt=number of transmission line feeders me=number of radial ground wires N =mw/ m: 0=angle s spacing between wires of a plane, parallel wire, grating Zo'=characteristic impedance of plane grating over infinitely conductive sheet Zo=characteristic impedance of two parallel sheets element above the earth or element, V(

Authorities for certain of the formulae (5 Pistolkors, Theory of Circular Diffraction Antenna, Proc. IRE, January 1948, Equation 8.

(l0) McLachlan, Bessel Functions for Engineers, 1934 edition, Equations 77, 79, 80. Based on assumptions discussed in J. A. Stratton, Electromagnetic Theory, first edition, pp. 5335 34.

(14), (15) as defined by G. N. Watson, Theory of Bessel Functions, second edition.

The invention claimed is:

1. An antenna system for use with a given ground plane element including a conductive surface element of substantially annular configuration having inner and outer boundaries, the surface of said element being arranged substantially parallel to said ground plane element, and means to couple radio frequency apparatus between'said agree-4e 9 ground plane element and 'said annular conductive surface element at the inner boundary only.

2. An antenna system for use in conjunction with an effectively infinite ground plane element, including a conductive surface element of annular configuration having inner and outer boundaries, the conductive surface being arranged substantially parallel to the ground plane, the outer boundary of said conductive surface element being spaced from said ground plane element by a distance small with respect to the transverse dimensions of said conductive surface element, and means to couple radi'o frequency apparatus between said ground plane element and said conductive surface element at the inner boundary only.

'3. An antenna system having a plurality of wires radially arranged above the earth, a loop of wire connecting the outer ends of said wires together, a portion of said wires being connected to earth beneath the center of said loop, radio frequency apparatus being connected between the inner ends of the remainder of said wires and the earth.

'4. -An antenna system including a conductive sheet constituting a ground plane and having an aperture therein, a plurality of elongated conductive elements radially arranged in said aperture about the center thereof, the inner ends of said conductors defining a central aperture, the outer ends of said conductive elements being interconnected and forming one edge of a slot formed with the edge of the first said aperture in said conducrive sheet, conductive wall members behind the first said aperture and connected to said conductive sheet to form a cavity resonator with said conductive elements, and means to couple radio frequency apparatus between said conductive elements and said conductive sheet.

5. An antenna system for use with a given ground plane element, including a pair of concentric wire rings lying in a plane substantially parallel to said ground plane element, a plurality of radially arranged wires connected to said concentric wire rings at spaced points about the circumferences thereof, and means to connect radio frequency apparatus between the smaller wire ring to said ground plane element.

6. An antenna system including a plurality of elongated conductors radially arranged about a common center in a plane parallel to an effective infinite ground plane, means to connect the outer ends of said conductors together, means to connect the inner ends of alternate ones of said conductors to said ground plane, and means to connect radio frequency apparatus between said ground plane and the inner ends of the remainnig ones of said conductors, the last said means comprising a coaxial transmission line having a conductive sheath bonded to said ground plane and a center conductor, said inner ends of said remaining conductors being connected to said center conductor and arranged to form a conical surface of revolution.

7. An antenna system for use with a given ground plane element including a plurality of wires arranged to constitute a conductive surface element having a substantially annular configuration, the surface of said element being arranged parallel to said ground plane element, and means to couple radio frequency apparatus between said elements.

8. An antenna system for use with a ground element of given conductivity including a conductive surface element constituted by a plurality of wires arranged in a substantially annular configuration, the surface of said element being arranged parallel to said ground, and means to couple radio frequency apparatus between said elements.

9. An antenna system for use with a given ground plane element, including a plurality of wires radially arranged with respect to a central point and terminating short of said central point to form an aperture thereabout, each of said plurality of wires being connected to said ground plane element at the ends thereof nearest said central point, and at least one further wire radially arranged with 1 0 respect to said point and being connected to radio fre quency transducer apparatus at the end nearest said point, the ends of all of said Wires remote from said central point being joined together.

10. An antenna system having a plurality of wires radially arranged in an aperture in the surface of a conductive ground plane element, a loop of wire connecting the outer ends of said wires together, a cavity resonator arranged behind said aperture, a portion of said wires being connected to a wall of said resonator behind the center of said loop, radio frequency apparatus being connected between the inner ends of the remainder of said wires and said wall of said resonator.

11. An antenna system having a plurality of wires radially arranged about a central point and terminating short of said central point, a loop of wire connecting the outer ends of said wires together, non-adjacent ones of said wires being connected together at the ends nearest said central point to form one junction, the remainder of said wires located between said non-adjacent wires being connected together at said central point to form another junction, and means to couple radio frequency apparatus between said junctions.

12. An antenna system including a plurality of elongated conductors radially -arranged about a common center in a plane parallel to an effective infinite ground plane, means to connect the outer ends of said conductors together, means to connect the inner ends of certain ones of said conductors taken in regular order about said center to said ground plane, and means to connect radio frequency apparatus between said ground plane and the inner ends of the remaining ones of said conductors.

13. An antenna system includin a plurality of elongated -conductors radially arranged about a common center in a plane parallel to an elfe'ctive infinite ground plane, means to connect the outer ends of said conductors together, further conductors connected to the inner ends of certain ones of said conductors taken in regular order about said center and arranged in the surface of a right cone having its base at said inner ends and its apex adjacent said ground plane, and means to connect radio frequency apparatus between said ground plane and the apex of said cone, the remaining ones of said conductors having the inner ends thereof connected to said ground plane.

14. An antenna system including a plurality of e'longated conductors radially arranged about a common center in a plane parallel to an effective infinite ground plane, means to connect the outer ends of said conductors together, further conductors connected to the inner ends of certain ones of said conductors taken in regular order about said center and arranged in the surface of a right cone having its base projected below said inner ends and its apex adjacent said ground plane, and means to connect radio frequency apparatus between said ground plane and the apex of said cone, the remaining ones of said conductors having the end thereof connected to said ground plane.

15. An antenna system for use in conjunction with an effectively infinite ground plane element, including (n+1)m conductors radially arranged with respect to a common center to define a surface element of revolution having an aperture defined by the inner ends of said conductors, m and n being any integer, said surface element being arranged parallel to said ground plane element, the outer ends of said conductors being connected together. mn conductors being coupled to said ground plane, and means to couple radio frequency apparatus between said ground plane element and every lf-. z)th conductor, said means comprising m further conductors arranged in conical formation and connected to every l+n)th conductor at the base and having the apex connected to said radio frequency apparatus.

16. An antenna system including a conductive sheet constituting a ground plane and having an aperture there-- in, a cavity resonator formed behind said aperture, a plurality of elongated conductors radially arranged in said aperture and connected together at the outer ends thereof, a portion of the inner ends of said conductors being connected in regular order to the wall of said resonator behind said aperture and the remainder being connected to a common junction point, and means to couple radio frequency apparatus between said sheet and said common junction point.

17. An antenna system for use with a given ground plane element, including a plurality of elongated conductors radiating from a central point above said given ground plane element to define a surface of revolution having an aperture defined by the inner ends of said conductors through which the axis of revolution passes, the outer ends of said conductors being interconnected, and means to couple transducer apparatus between at least a portion of said conductors and said given ground plane element.

18. An antenna system for use with a given ground plane element, including a plurality of elongated conductors radiating from a central point above said given ground plane element to define a surface or revolution having an aperture defined by the inner ends of said conductors, the axis of revolution passing through said aperture, the outer ends of said conductors being interconnected, means to couple transducer apparatus between a portion of said conductors and said given ground plane element, and means connecting the inner ends of the remainder of said conductors to said ground plane element.

19. An antenna system for use with a given ground plane element, including a plurality of elongated conductors radiating from a central point above said given ground plane element to define a surface of revolution having an aperture defined by the inner ends of said conductors, the axis of revolution passing through said aperture, the outer ends of said conductor being interconnected, means to couple transducer apparatus between the inner ends of ones of said conductors taken in regular order about said aperture and said given ground plane element and means to connect the inner ends of the remainder of said conductors to said given ground plane element, the outer ends of said conductors being closer to said given ground plane element than the inner ends.

20. An antenna system for use with a given ground plane element, including a plurality of elongated conductors radiating from a central point above said given ground plane element to define a surface of revolution having an aperture defined by the inner ends of said conductors, the axis of revolution passing through said aperture, the outer ends of said conductor being interconnected, means to couple transducer apparatus between the inner ends of ones of said conductors taken in regular order about said aperture and said given ground plane element and means to connect the inner ends of the remainder of said conductors to said given ground plane element, the outer ends of said conductors being lower than the inner ends thereof.

21. An antenna system for use with a given ground plane element, including a plurality of elongated conductors radiating from a central point above said given ground plane element to define a surface of revolution having an aperture defined by the inner ends of said conductors, the axis of revolution passing through said aperture, the outer ends of said conductors being interconnected, means to couple transducer apparatus between the inner ends of ones of said conductors taken in regular order about said aperture and said given ground plane element, and means to connect the inner ends of the remainder of said conductors to said given ground plane element.

22. An antenna system for use with a given ground plane element, including an efiective current sheet annulus constituted by a plurality of wires extending radially from the circle defining the inner boundary of the annulus and terminating at a further wire lying substantially on the circle defining the outer boundary of the annulus, and means to couple radio frequency apparatus between said given ground plane element and said current sheet annulus at the inner boundary only thereof.

References Cited in the file of this patent UNITED STATES PATENTS 760,463 Marconi May 24, 1904 767,974 Stone Aug.'16, 1904 1,595,166 Scheller Aug. 10, 1926 2,180,855 Wundt et al. Nov- 21, 1939 2,665,380 Hickson et a1. Jan. 5, 1954 FOREIGN PATENTS 194,365 Great Britain Mar. 5, 1923 176,803 Great Britain July 10, 1923 248,597 Great Britain Mar. 11, 1926 

